Problem: $-6st + 8su - 4s - 4 = 5t + 8$ Solve for $s$.
Solution: Combine constant terms on the right. $-6st + 8su - 4s - {4} = 5t + {8}$ $-6st + 8su - 4s = 5t + {12}$ Notice that all the terms on the left-hand side of the equation have $s$ in them. $-6{s}t + 8{s}u - 4{s} = 5t + 12$ Factor out the $s$ ${s} \cdot \left( -6t + 8u - 4 \right) = 5t + 12$ Isolate the $s$ $s \cdot \left( -{6t + 8u - 4} \right) = 5t + 12$ $s = \dfrac{ 5t + 12 }{ -{6t + 8u - 4} }$